This invention relates to a detector of electromagnetic radiation. More particularly, this invention relates to an electromagnetic radiation detector which can detect the location as well as measure the energy of a source of radiation, without the use of a collimator and with the use of only a single photomultiplier tube.
Electromagnetic radiation detectors commonly in use for locating a source of radiation employ pinhole collimators of lead or some other inactive, inert material. A disadvantage of these detectors is that the detection efficiency is poor due to the collimator and removal of the collimator results in inadequate spatial resolution, i.e., location of the source of radiation in an x, y, z coordinate system. The problem can readily be appreciated by reference, for example, to a problem in health physics. In health physics, there is sometimes the need to locate the site of deposition of plutonium, a low-energy photon emitter, in the lungs for a more refined estimate of body burden versus external in vivo counting rate. A "gamma camera" was used to count a relatively heavily internally contaminated individual in an attempt to get information on the site of deposition. It was found that with the lead collimator in place, the count rate was too low to be meaningful, and without the collimator there was almost no resolution.
There have at various times been proposed in the prior art the use of an array of scintillators or radiation detectors to determine the direction or location of a source of radiation. Examples are U.S. Pat. Nos. 3,436,539; 3,539,806; and 3,594,577. However, in U.S. Pat. No. 3,436,539, radiation shielding and three photomultiplier tubes are required; in U.S. Pat. No. 3,539,806, a plurality of light reflecting partitions and a plurality of photomultiplier tubes are required; and in U.S. Pat. No. 3,594,577, a collimator having a plurality of holes and a plurality of photomultiplier tubes are required.